This invention relates generally to continuous heat transfer systems of the kind used in commercial settings to produce pre-cooked food products. More particularly, the invention relates to transfer mechanisms and devices used to transfer food product into and out of these continuous heat transfer systems such as fryers, water cookers, steamers, microwave, infrared systems, and linear and spiral ovens.
The development of continuous ovens in the food industry has grown significantly over the past 20 years, along with the increased demand for pre-cooked food products and the range of those products. Products ranging from roasted vegetables to teriyaki chicken and other marinated chicken products are now cooked on continuous ovens and an increasing number of food products are cooked in continuous fryers, water cookers, steamers, microwave, and infrared systems. Practically every heat transfer system now known to man is utilized on food products.
A constant challenge for the manufacturers of this equipment is the transfers into and out of the continuous heat transfer system. By way of example, consider the transfer of a partially cooked sausage patty being transferred off the end of a spiral oven cook belt in a first (par-cook) zone and transferred in-line to a second spiral oven to be fully cooked. Those skilled in the art would recognize that the transfer mechanism used in a spiral oven application can apply to any continuous heat transfer system or process.
The patties are nominally 3/16″ thick and 3¾″ in diameter, weighing 1.3 oz. When in batter form, the sausage must be formed into patties at a temperature of 25° F. to 28° F. Forming the patties below the freezing point greatly aids in the transfer of the product into the spiral oven. Above this temperature, the batter is more fluid and will not form with a consistent shape. Like any meat product, the more each patty is cooked, the more the protein sets up and the more rigid the product becomes. Therefore, fully cooking the patties helps the product transfer more easily but, like par-cooked product, fully cooked product can also adhere to the belt.
Some spiral oven manufacturers, such as GEA and Marel, seek to overcome this problem by having one belt that passes through two spirals, effectively eliminating the transfer between the first and second zones. However, this solution restricts the residence time in each zone to a fixed formula. For example, if Zone 1 has 100 meters of belt and Zone 2 has 100 meters of belt, the residence time in each zone must be equal. Similarly, if the belt ratio in each zone is different, for example 70 to 30, then the overall time is fixed to a 70/30 split.
Residence time in each zone can independently vary by using a transfer system like one provided by Unitherm Food Systems, Inc. (“Unitherm”) which allows each zone to have a separate belt. The Unitherm system uses a driven roller located at the end of the heat transfer equipment, with a small gap between the belt and the roller. The gap eliminates metal-to-metal contact that can create metal shavings or oxidation that develops a black oil-like substance that emulsifies between the metal surfaces. The reliability of this transfer system is critical because if it fails on any part of the belt, product can be ruined during the transfer (or failed transfer) and not recovered.
Other Unitherm transfer systems include a close, tight-turn radius shafts with belts. Again, there is a small gap between the belt and the shafts. Occasionally a fixed scraper is used that is in contact with the belt. This type of transfer, while effective, can wear out quickly and can occasionally jam against the belt.
Because spiral oven belts expand and contract—collapsing on the inside and, in some configurations, expanding on the outside—the belts can form temporary bumps, or peaks and valleys, when the links do not rest as intended or as the belt links travel around the curvature of a shaft. The rate of expansion and contraction at the discharge roller can also vary.
The belts are typically of the kind made by Ashworth Brothers and Cambridge Belt Co. (see FIG. 1 for a typical oven belt pattern). As the belt turns around the end of the roller/sprocket at the discharge or exit end of the belt, the belt takes a polygonal shape due to the presence of rigid links, that is, turning in a manner similar to rotating a hexagon. Therefore, the radius is not smooth. Additionally, the temperature at this end can be in the range of 200° F. to 450° F., depending on the operating temperature of the oven. In processes that make use of flame grills, the temperature at the exit end of the belt can be as high as 800° F.
There is a need for a transfer system that can reliably transfer par-cooked meat product and transfer product off the hot, non-smooth radius, end-portion of the belt that is in a variable state of collapse and, potentially, with a temporary bump, peak, or valley in the belt.